156 A. W. BENNETT. 
resembling the resting-spores of M. racemosus ; but they had 
no power of germinating; after a few days they burst and 
perished, a thick lump of protoplasm escaping from these, 
which soon became dark in colour. : 
The change in the form of the filaments of Mucor racemo- 
sus already mentioned, which makes the later generations so 
closely resemble true yeast, depends on the fact that under 
the influence of the fungus the infusion gradually becomes 
acid from its gradual saturation with carbonic acid. ‘That it 
is the carbonic acid which causes the filaments to become 
shorter and more spherical may be proved by passing a 
stream of this gas through the fluid, when the effect stated 
is seen to be produced in the successive products of the same 
cell. If for the carbonic acid a stream of hydrogen gas is 
then substituted, the normal filaments are again produced. 
Although other Mucorini do not possess the peculiarity of 
putting out yeast-like filaments under the influence of car- 
bonic acid, the same effect is produced in some of them by 
vegetable acids. If Mucor (Thamnidium) elegans or M. 
Mucedo is grown in citron-juice to which a little citric acid 
is added, the spores swell up into large globes which put out 
a number of lateral offshoots. ‘These shoots again assume a 
globular form ; and the process goes on until the whole mass 
dies or puts out a few sporangiophores, this latter occurring but 
rarely. But if, before the mass perishes, as much ammonia 
is added as suffices nearly to neutralise the solution, the 
short spherical shoots again put out filaments of the normal 
form. 
The liability of the Mucorini, especially M. racemosus, to 
assume the form now described, has been the source of nume- 
rous errors. Bail! and others assert that Mucor passes over, 
in a fluid capable of fermentation, into yeast (Saccharomyces). 
Reess’ pointed out the inaccuracy of this statement, but him- 
self asserted that in such a fluid as e.g. a solution of grape- 
sugar, Mucor Mucedo and racemosus assumed a yeast-like 
appearance. ‘This assertion is again not correct, since in such 
fluids both these species produce only the normal germinating 
filaments, which are renewed from the periodically formed 
resting-spores, and the filaments produced from these assume 
amore and more yeast-like appearance as the solution be- 
comes gradually saturated with carbonic acid. The assumed 
genetic connection between Mucor and Saccharomyces is 
1 *Mittheilungen tiber das Vorkommen u. die Entwicklung einiger 
Pilzformen. Danzig, 1867. 
? « Aleoholgahrungspilze.’ Leipzig, 1870. 
